"Security around all the airports have been strengthened and we have taken all the measures that are required in the wake of the alert from intelligence agencies," official sources said here on Sunday.

All anti-hijacking measures have been put in place, they said, adding that passengers' checking has also been beefed up at some of the major airports, including Indira Gandhi International Airport here.Authorities have also put in place multi-level checking at the airport, and even staff members are being screened thoroughly. The ground staff has been asked to check all cabin baggage once boarding is completed.

The airport staff has been asked to carry out checking of the cabin baggage once the boarding is competed and even the airport staff is being thoroughly checked by the airport security personnel, they said.

The alert has been issued in the run-up to the Republic Day and US President Barack Obama's visit to India. Obama will be the chief guest at the Republic Day celebrations.The hijack bid could be similar to the one in 1999, in which terrorists hijacked Indian Airlines flight IC 814 and took it to Kandahar, according to the intel input.

The alert comes a day after Air India's Kolkata office received an anonymous phone call informing that an Air India plane would be hijacked.

A senior Kolkata police official said it was a brief call in Bengali threatening that an Air India flight would be hijacked. The official, however, did not specify which flight would be targeted.

Senior officials of Bureau of Civil Aviation Security, CISF and AAI held a meeting in Kolkata on Saturday night to review the security measures.